Reduction of internal combustion engine exhaust emissions is a fundamental problem confronting the automotive industry worldwide. Nitrogen oxide (“NOx”) emissions are a class of engine exhaust emissions which are coming under increasingly strict regulatory scrutiny because of their asserted affect on the environment. NOx emissions from internal combustion engines are, for example, asserted to be precursors in the formation of ozone and are further asserted to be responsible for the formation of other types of air pollution, such as smog.
Diesel engines present a further problem for the automotive and transportation industry in that the exhaust emissions from these type of engines typically include large amounts of particulates together with NOx. The particulate emissions are present in the black smoke discharged from the engine. Currently, diesel engine particulate emissions can be controlled by the use of filters or catalytic converters. While these emission-control devices are effective in decreasing particulate emissions, they do not appear to be effective in reducing NOx emissions.
Attempts have been made to reduce NOx and particulate emissions from internal combustion engines. However, these known emission control systems and strategies have associated disadvantages.
One known method of reducing NOx emissions involves treating the post-combustion exhaust emissions. For example, PCT patent publication WO 98/22209A1, (Peterhoblyn et al.) discloses the use of selective catalytic reduction (SCR) in which an aqueous urea solution is introduced from a tank into the engine exhaust manifold. The urea-containing exhaust gas is then directed to a foraminous structure that traps any water or urea that has not been gasified. Subsequently, the exhaust gas is directed through an NOx-reducing catalyst structure. PCT patent publication WO 99/01205 (Marko et al.) discloses a further type of SCR in which gaseous ammonia is introduced to the post combustion exhaust gas followed by treatment with a reduction catalyst.
U.S. Pat. Nos. 5,783,160 (Kinugasa et al.), 5,992,141 (Berriman et al.) and 5,609,026 (Berriman et al.) also disclose a type of engine exhaust treatment in which gaseous ammonia is introduced to the post combustion exhaust gas followed by treatment with a catalyst. Other publications disclosing apparatus for treating engine exhaust to reduce NOx emissions, such as catalytic converters, include U.S. Pat. Nos. 5,522,218 (Lane et al.) and 5,791,139 (Takeshi et al.).
All of the aforementioned NOx-reducing systems are disadvantageous because of the extensive and costly mechanical structure required for operation of the systems.
Another method of treating post-combustion exhaust emissions involves a process known as exhaust gas recirculation (EGR). Such a system is disclosed in PCT patent publication WO 97/04045A1 (Peterhoblyn et al.) which describes the use of EGR, or an engine timing modification, in combination with a particulate trap and a platinum group metal catalyst composition. While possibly effective in reducing NOx emissions, this system disadvantageously requires costly mechanical and catalytic components.
Yet another known method of reducing NOx emissions involves introduction of a selective reducing agent directly into the engine combustion chamber such as shown in U.S. Pat. No. 5,584,265 (Rao et al.). According to Rao, a selective reducing agent such as ammonia, hydrazine, or cyanuric acid is injected into the interior of the piston-cylinder assembly with a mechanical material-feed apparatus. The reducing agent is stored in a tank within the vehicle. The reducing agent reacts during combustion to produce an exhaust stream with a reduced concentration of NOx. The system of the Rao patent disadvantageously requires the use of complex and costly mechanical apparatus in order to introduce the correct amount of reducing agent into the combustion chamber.
Various fuel additives and formulations have been proposed as a means of reducing NOx emissions. Certain of these compositions are provided to solubilize water in the fuel thereby cooling the fuel charge and reducing the NOx emissions. One such example is provided in PCT patent publication WO 98/17745 (Hazel et al.) which discloses prior work of two of the present applicants. The Hazel invention provides a surfactant to solubilize water present in the fuel. The surfactant comprises an alkoxylated alcohol, a diethanolamide and a polyethylene glycol monoester. PCT patent publication WO 00/15740 (Daly et al.) discloses an emulsified water-blended fuel composition containing a liquid fuel, water, an emulsifier, an amine salt which may function as an emulsion stabilizer or combustion modifier. These compositions, while efficacious in certain applications, are not optimally effective in reducing NOx emissions and are not effective in solubilizing NOx-reducing agents.
Another approach to general reduction of emissions from diesel fuel involves use of a surfactant system to stabilize anhydrous or hydrous ethanol in diesel fuel thereby reducing the overall fuel hydrocarbon-content. U.S. Pat. No. 6,017,369 (Ahmed) discloses a solubilized diesel fuel composition including diesel fuel, ethanol, an alkyl ester of a fatty acid, a stabilizing additive and an optional co-solvent. The stabilizing additive is reportedly provided to homogenize the constituents of the fuel composition. The stabilizing agent is reported to be either (1) a mixture of ethoxylated alcohols, a cetane booster and a demulsifier or (2) a mixture of ethoxylated alcohols, an amide and an ethoxylated fatty acid. While reportedly effective in reducing diesel fuel emissions generally (as a result of reducing the percentage of diesel fuel in the composition), the Ahmed composition does not disclose any specific assertion of NOx or particulate emission reduction.
U.S. Pat. No. 5,746,783 (Compere et al.) discloses a microemulsion of urea or a triazine which, when added to a base diesel fuel composition, is said to decrease the amount of NOx emissions from diesel engines. The microemulsion comprises the urea or triazine mixed with t-butyl alcohol, water, oleic acid and ethanolamine. The composition of the Compere patent is disadvantageous because it requires higher levels of urea than are needed to reduce NOx. Moreover, the composition requires higher levels of solubilizing agent to maintain the urea in the composition than are practical or economical. It is expected that a fuel containing the composition would have lower BTU and a lower cetane number/index with resulting disadvantages, such as potentially causing the fuel to be outside of standard specifications. In addition it can be demonstrated that the use of a fuel containing this composition would not be clear or homogeneous at the higher fuel dilutions utilized in the industry.
In addition to the need to provide an improved manner of reducing NOx and particulate emissions from internal combustion engines, a fuel additive or formulated fuel should be useful in overcoming other problems associated with fuel technology. The additive should be such that the fuel formulation is a stable, homogenous mixture across a broad temperature range. Further, low sulfur and ultra low sulfur diesel fuels presently being manufactured lack lubricity as a result of the low sulfur content of the fuels. Reduced lubricity contributes to engine wear and reduces the distance that the vehicle can travel per unit volume of fuel. It would be desirable for the fuel additive or formulated fuel to improve lubricity in these low and ultra low sulfur fuels.
Moreover, a significant material-handling issue confronting the possible use of non-ionic surfactants in fuel compositions involves the lack of liquidity of many non-ionic surfactants. Specifically, such non-ionic surfactants are present in a gel state when blended with water. Solvents are required to impart the desired viscosity to such surfactant compositions. The addition of solvents adds to the cost of transport and, potentially, may create difficulties in mixing the additive with the fuel. Preferably, therefore, the surfactant should be selected so that the host fuel itself could be used as the solvent. This would permit formulation of a fuel additive concentrate which could be delivered and easily cold splash blended with the host fuel.
An improved fuel additive which, when blended with fuels, would reduce levels of fuel NOx and particulate emissions when the fuel is burned in an internal combustion engine without materially affecting the BTU content of the fuel, which could be used without mechanical modification of the vehicle, which improves lubricity of the fuel and is easy to formulate and handle would represent an important advance in the art.